[PDF] [PDF] Chapter 7: Arrays Lab Exercises

Chapter 7: Arrays 125 int loc; switch(choice) { case 0: System.out.println("Bye!"); break; case 1: System.out.println("How big should the list be?"); int size = scan.nextInt(); list = new IntegerList(size); list.randomize(); break; case 2: list.print(); break; default: System.out.println("Sorry, invalid choice"); } } //---------------------------- // Print the user's choices //---------------------------- public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Create a new list (** do this first!! **)");

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A Shopping Cart

In this exercise you will complete a class that implements a shopping cart as an array of items. The file Item.java contains the

definition of a class named Item that models an item one would purchase. An item has a name, price, and quantity (the

quantity purchased). The file ShoppingCart.java implements the shopping cart as an array of Item objects.

1. Complete the ShoppingCart class by doing the following:

a. Declare an instance variable cart to be an array of Items and instantiate cart in the constructor to be an array holding

b. Fill in the code for the increaseSize method. Your code should be similar to that in Listing 7.8 of the text but instead

c. Fill in the code for the addToCart method. This method should add the item to the cart and update the totalPrice

2. Write a program that simulates shopping. The program should have a loop that continues as long as the user wants to

shop. Each time through the loop read in the name, price, and quantity of the item the user wants to add to the cart. After

adding an item to the cart, the cart contents should be printed. After the loop print a "Please pay ..." message with the

Chapter 7: Arrays 127 public double getPrice() { return price; } // ------------------------------------------------- // Returns the name of the item // ------------------------------------------------- public String getName() { return name; } // ------------------------------------------------- // Returns the quantity of the item // ------------------------------------------------- public int getQuantity() { return quantity; } } // *********************************************************************

* // ShoppingCart.java // // Represents a shopping cart as an array of items // *********************************************************************

* import java.text.NumberFormat; public class ShoppingCart { private int itemCount; // total number of items in the cart private double totalPrice; // total price of items in the cart private int capacity; // current cart capacity // ----------------------------------------------------------- // Creates an empty shopping cart with a capacity of 5 items. // ----------------------------------------------------------- public ShoppingCart() { capacity = 5; itemCount = 0; totalPrice = 0.0; } // ------------------------------------------------------- // Adds an item to the shopping cart. // ------------------------------------------------------- public void addToCart(String itemName, double price, int quantity)

{ } // ------------------------------------------------------- // Returns the contents of the cart together with // summary information.

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String contents = "\nShopping Cart\n";

Chapter 7: Arrays 129

Averaging Numbers

As discussed in Section 7.4 of the text book, when you run a Java program called Foo, anything typed on the command line

1. Write a program Average.java that just prints the strings that it is given at the command line, one per line. If nothing

2. Modify your program so that it assumes the arguments given at the command line are integers. If there are no

arguments, print a message. If there is at least one argument, compute and print the average of the arguments. Note

that you will need to use the parseInt method of the Integer class to extract integer values from the strings that are

passed in. If any non-integer values are passed in, your program will produce an error, which is unavoidable at this

3. Test your program thoroughly using different numbers of command line arguments.

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Exploring Variable Length Parameter Lists

The file Parameters.java contains a program to test the variable length method average from Section 7.5 of the text. Note

1. Compile and run the program. You must use the -source 1.5 option in your compile command.

2. Add a call to find the average of a single integer, say 13. Print the result of the call.

3. Add a call with an empty parameter list and print the result. Is the behavior what you expected?

4. Add an interactive part to the program. Ask the user to enter a sequence of at most 20 nonnegative integers. Your

program should have a loop that reads the integers into an array and stops when a negative is entered (the negative

number should not be stored). Invoke the average method to find the average of the integers in the array (send the

5. Add a method minimum that takes a variable number of integer parameters and returns the minimum of the

System.out.println ("mean1 = " + mean1);

System.out.println ("mean2 = " + mean2);

Chapter 7: Arrays 131

Magic Squares

One interesting application of two-dimensional arrays is magic squares. A magic square is a square matrix in which the sum

of every row, every column, and both diagonals is the same. Magic squares have been studied for many years, and there are

some particularly famous magic squares. In this exercise you will write code to determine whether a square is magic.

File Square.java contains the shell for a class that represents a square matrix. It contains headers for a constructor that gives

the size of the square and methods to read values into the square, print the square, find the sum of a given row, find the sum

of a given column, find the sum of the main (or other) diagonal, and determine whether the square is magic. The read method

is given for you; you will need to write the others. Note that the read method takes a Scanner object as a parameter.

File SquareTest.java contains the shell for a program that reads input for squares from a file named magicData and tells

whether each is a magic square. Following the comments, fill in the remaining code. Note that the main method reads the

size of a square, then after constructing the square of that size, it calls the readSquare method to read the square in. The

You should find that the first, second, and third squares in the input are magic, and that the rest (fourth through seventh) are

132 Chapter 7: Arrays

Chapter 7: Arrays 133 // **************************************************************** // SquareTest.java // // Uses the Square class to read in square data and tell if // each square is magic. // // **************************************************************** import java.util.Scanner; public class SquareTest { public static void main(String[] args) throws IOException {

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Chapter 7: Arrays 135

A Shopping Cart Using the ArrayList Class

In this exercise you will implement a shopping cart using the ArrayList class. The file Item.java contains the definition of a

class named Item that models an item one would purchase (this class was used in an earlier lab). An item has a name, price,

and quantity (the quantity purchased). The file Shop.java is an incomplete program that models shopping.

1. Complete Shop.java as follows:

b. Fill in the statements in the loop to add an item to the cart and to print the cart contents (using the default toString in

2. You should have observed two problems with using the default printing for the cart object: the output doesn't look very

good and the total price of the goods in the cart is not computed or printed. Modify the program to correct these

b. computes the total price of the items in the cart (you need to use the getPrice and getQuantity methods of the Item

3. Compile and run your program.

ArrayList cart = new ArrayList();

Item item;

String itemName;

Scanner scan = new Scanner(System.in);

String keepShopping = "y";

System.out.print ("Enter the unit price: ");

System.out.print ("Enter the quantity: ");

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System.out.print ("Continue shopping (y/n)? ");

Chapter 7: Arrays 137

A Polygon Person

A polygon is a multisided closed figure; a polyline is a line with an arbitrary number of segments. Both polygons and

polylines are defined by a set of points, and Java provides graphics methods for both that are based on arrays. Read section

7.8 in the text and study the Rocket example in Listing 7.16 & 7.17.

Files DrawPerson.java and DrawPersonPanel.java contain a program that draws a blue shirt. Copy the programs to your

1. Draw pants to go with the shirt (they should be a different color). You will need to declare pantsX and pantsY arrays like